Self-stabilizing base for pressurized bottle

ABSTRACT

A blow molded, biaxially oriented plastic container with a bottom portion including an axially, inwardly directed generally conical portion, a standing section on which the container rests, a heel portion joining the bottom portion and container body portion, and a hinge portion joining the conical portion and the standing section, wherein the wall thickness of the hinge portion is greater than the wall thickness of the heel portion.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 397,970, filed Aug. 24, 1989 now U.S. Pat. No. 4,969,563.

BACKGROUND OF THE INVENTION

This invention relates to thermoplastic containers for the retention offluids under pressure, such as carbonated beverages and the like. Thesecontainers may be prepared from a perform or parison which may beinjection molded, followed by blow molding said parison into a suitablyshaped container. A typical thermoplastic material is poly (ethyleneterephthalate) or PET, although others can be used.

The container configuration generally includes a neck portion with acap-receiving means, a shoulder portion depending therefrom, a side wallor main body portion depending from the shoulder portion and a bottomwall joined to the side wall. In many of these containers the bottomwall has a champagne bottle bottom configuration with an internal,axially inwardly directed, generally conical part.

The bottom wall of these containers represents a weak part of thecontainer. It is desirable to provide a bottom shape capable of servingas a stable bottom support.

Thus, beverage under pressure within the container has a tendency todeform the bottom wall, as for example everting the inwardly directedconical part to render the bottom wall unstable.

Many attempts have been made to overcome these problems while at thesame time providing a construction which is inexpensive and economicalto process. For example, U.S. Pat. No. 3,881,621 provides a ribbedstrengthening at the bottom wall; however, this still providesinsufficient strengthening. U.S. Pat. No. 4,134,510 provides a pluralityof concentric annular strengthening ribs and a plurality of additionalintersecting radial ribs in a complex and expensive procedure. U.S. Pat.Nos. 4,620,639, 4,261,948, 4,603,831, and 4,334,627 utilize a pluralityof inwardly projecting rigid ribs so that the bottom wall is thicker atthe ribbed portion than the remainder of the bottom wall; however, thisresults in a container having substantial and sharply defineddifferences in wall thickness with resultant sharp temperaturedifferences in processing presenting difficult, processing controlproblems. U.S. Pat. No. 4,865,206 utilizes a plurality of wall portionsextending downwardly from the bottom wall forming hollow legs extendingbelow the bottom wall having planar feet which are inclined upwardly andinwardly from the outer edges of the feet. While most of the aboveimprove the resistance to eversion, they are limited to configurationsresulting in insufficient stability and insufficient compressivestrength of the bottle.

U.S. Pat. No. 4,785,948, By Herbert Strassheimer, teaches the use of animproved plastic preform for forming blow molded plastic containers andresultant improved plastic containers wherein the container has atubular body portion adjacent a bottom portion and extending onto thebottom portion having circumferentially spaced radially extendingcontinuous alterations in wall thickness. The preform is characterizedby the bottom structure thereof having a plurality of faces capable offorming a blow molded plastic bottle with a bottom portion having saidcircumferentially spaced radially extending continuous alterations inwall thickness with a regularly undulating cross section across thecircumference thereof, wherein said alterations in wall thickness areprogressive and gradual. While the teaching of U.S. Pat. No. 4,785,948provides a stable and reinforced bottom wall configuration which issimple in construction and inexpensive to prepare and a preform which issimilarly convenient and expeditious to prepare, such improvements areat times insufficient in the case of large bottles Thus, it is desirableto further improve the characteristics of the resultant container,especially the resultant bottom regions corresponding to the intersectsof the said faces of the preform. It is highly desirable to enhance theproperties at this region and to increase the stability of the filledand pressurized container.

It is therefore a principal object of the present invention to providean improved plastic container having a reinforced bottom wallconfiguration, that is stable when filled with a beverage underpressure.

It is a further object of the present invention to provide an improvedcontainer as aforesaid which is simple in construction and inexpensiveto prepare and which provides a stable base configuration.

Further objects and advantages of the present invention will appearhereinbelow.

SUMMARY OF THE INVENTION

In accordance with the present invention it has now been found that theforegoing objects and advantages may be readily obtained. The blowmolded, biaxially oriented plastic container of the present inventioncomprises: a neck portion defining an opening; a tubular body portiondepending therefrom; an integral bottom portion depending from thetubular body portion; an axially, inwardly directed, generally conicalportion of said bottom portion, wherein said bottom portion includes astanding section on which the container rests in the upright condition;wherein said bottom portion includes a heel portion joining the standingsection and the body portion and a hinge portion joining the conicalportion and the standing section; said container having means includinga hinge portion wall thickness greater than the heel portion wallthickness wherein said heel portion moves outward and downward uponpressurizing the container to provide a stable bottom portion. Inaccordance with the present invention both the heel portion and theconical portion have a radius of curvature with the ratio of the radiusof curvature of the hinge portion to the radius of curvature of theconical portion varying from 0.75 to 2, and preferably from 1 to 1.6.

In a preferred embodiment, the hinge portion has a greater wallthickness than the body portion. Also, the conical portion includes anupper region and preferably the wall thickness of the hinge portion isgreater than the wall thickness of the upper region of the conicalportion. The heel portion is preferably thinner than the upper region ofthe conical portion.

It is particularly preferred to provide the container with continuousalterations in wall thickness with a regularly undulating cross sectionacross the entire circumference of the inside wall face which isprogressive and gradual, wherein said continuous alterations in wallthickness are provided on the tubular body portion adjacent the bottomportion and extending onto the bottom portion. The preform from whichthe container is prepared preferably has an outside wall face and aninside wall face, with the inside wall face of the tubular body portionadjacent the bottom structure and extending onto the bottom structurehaving a plurality of faces with terminal portions thereof and withscallop-shaped segments connecting the terminal portions of each faceadapted to deform upon exposure to stresses prior to deformation of thefaces and thereby become subject to an increased rate and degree oforientation. The thinner portions of the continuous alterations in wallthickness are preferably extended and thereby bi-axially oriented due tothe aforesaid provision of the scallops in the preform. The foregoingfeatures are described in copending U.S. patent applications Ser. No.262,781 and Ser. No. 354,461.

In accordance with the provisions of the present invention, theforegoing container has enhanced stability, good strengthcharacteristics and is simple, convenient and expeditious to prepare.

Further features and advantages of the container of the presentinvention will be discussed hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be more readily apparent when considered inconnection with the following illustrative examples wherein:

FIG. 1 is a sectional view of a preform for preparing the container ofthe present invention;

FIG. 2 is an enlarged sectional view along lines 2--2 of FIG. 1;

FIG. 3 is a partial sectional view taken through a mold for molding thecontainer of the present invention and having associated therewith apreform similar to the preform of FIG. 1 which is to be stretched andblown therein to form a container of the present invention;

FIG. 4 is an elevational view of a container of the present inventionformed in FIG. 3;

FIG. 5 is an enlarged sectional view taken along lines 5--5 of FIG. 4,with the corresponding sectional view of FIG. 2 superimposed therein inphantom;

FIG. 6A is a partly schematic, enlarged sectional view of the bottomportion and adjacent tubular body portion of the container of FIG. 4 inthe empty condition;

FIG. 6B is a view similar to FIG. 6A with the container in thepressurized condition; and

FIG. 7 is a schematic illustration of the bottom portion and adjacenttubular body portion of the container of FIG. 4 in the empty conditionillustrating the radius of curvature of the hinge portion and the radiusof curvature of the conical portion.

DETAILED DESCRIPTION

Referring now to the drawings in detail, a plastic parison or preform 10is formed by injection molding from a synthetic resin which can bebiaxially oriented, as for example poly (ethylene terephthalate). Thepreform 10 has a neck portion 11 defining an opening 12 and it may beprovided with external threads 13 to serve as the site for attachment ofa cap on the finished, blow molded plastic container. The preform 10 hasa tubular body portion 14 depending from the neck portion 11 and anintegral bottom structure 15 depending from the tubular body portion.The preform 10 has an outside wall face 16 and an inside wall face 17.The inside wall face 17 of the tubular body portion 14 is provided witha thickened portion 18 which extends onto bottom structure 15 and ischaracterized by a plurality of faces 19, which may be flat as shown orcurved, with terminal portions thereof 19a. Scallop-shaped segments 20connect the terminal portions of each face 19. Three or more of saidflat or curved faces 19 may be used, although the hexagonalconfiguration of FIG. 2 is preferred. Alternately, for example, anoctagonal configuration may readily be employed. The bottom structure 15as shown in FIG. 1 may be flat or may be provided with an axiallyinwardly directed conical part 21 as shown in FIG. 3.

Compared to the preform typically used according to the known art, e.g.U.S. Pat. No. 4,785,948, the length "L" of thickened portion 18 isshortened and the depth of the scallop-shaped segments 20 may bedecreased as well. The greater the length "L", the more does thethickened portion of the base of the bottle blown from the preformextend outward, to the side wall and thus, the less the same portionwill be oriented, meaning undue brittleness. Similarly, the deeper thescallop 20, i.e., the thinner the wall at said scallops, the moreorientation will be obtained at the bottle regions corresponding to thescallops.

Thus, in order to obtain a high degree of orientation at the heel 50 ofthe bottle, the length "L" is reduced so as to limit the correspondingthick portions of the base to a region well inward of the heel, see FIG.6 and the discussion hereinbelow.

As shown in FIG. 1, thickened portion 18 includes a lower portion 18aadjacent the bottom structure having a wall thickness less than the wallthickness of the adjacent thickened portion 18. It has been found thatthis may be employed in order to save material costs without loss ofnecessary properties in view of the significant advantages obtained inaccordance with the present invention. Alternately, if desired, externalribs may be provided on the preform as disclosed in the aforesaid U.S.Pat. No. 4,785,948.

The thus formed preform is brought to a temperature at which blowmolding can be accomplished which may be done by heating a previouslyformed parison or forming the hot parison in line with the blow moldingoperation and suitably adjusting the temperature thereof. The heatedpreform is then placed in a blow mold having the configuration of thedesired container, to be described in greater detail below, as blow mold30 shown in FIG. 3 and while blowing compressed air thereinto, theinterior side of bottom portion 15 is pushed down by movable means 31 toeffect biaxial orientation. The blow mold 30 shown in FIG. 3 has aninternal configuration which allows the formation of a plastic container40 of the present invention (see FIG. 4) having a desired configurationas set forth herein.

Thus, blow molded plastic container 40 is formed having a neck portion41 defining an opening 42, a bottom portion 43, a tubular body portion44 interconnecting the neck portion 41 and the bottom portion 43. Neckportion 41 is provided with external threads 45 to serve as the site forattachment of a cap on the container, as with preform 10. The bottomportion 43 has an internal, axially inwardly directed generally conicalpart 46.

FIG. 5 shows a preferred embodiment of the present invention wherein theflat or curved faces form a hexagonal configuration. Scallop-shapedsegments 20 form the thinner portions 49a of the regularly undulatingcross-sectional configuration of the bottom portion of the containerwith 49 representing the thicker portions. Said segments may constituteparts of circles, to facilitate manufacture.

FIGS. 6A and 6B represent partly schematic, enlarged sectional views ofthe bottom portion 43 and adjacent tubular body portion 44 of thecontainer 40, wherein FIG. 6A shows the container in the empty conditionand FIG. 6B shows the container in the pressurized condition. The heelportion 50 of bottom portion 43 joins the bottom portion to the bodyportion 44. The bottom portion also includes a standing section 51 onwhich the container rests in the upright condition, and a hinge portion52 joining the conical portion 46 to the standing section.

In accordance with the present invention, the wall thickness of thehinge portion 52 is greater than the wall thickness of the heel portion50. Also, the wall thickness of the heel portion 50 is greater than thewall thickness of the body portion 44. Conical portion 46 includes anupper region 53, with the wall thickness of the hinge portion 52 beinggreater than the wall thickness of the upper region 53. The wallthickness of the heel 50 may be thinner than the wall thickness of theupper region. These relationships are shown schematically in FIG. 6A andare maintained in the pressurized container of FIG. 6B. Illustrativewall thickness ranges in the container of FIG. 6A are: heel--0.35 mm;hinge--3.2 mm; upper region of conical portion--2.2 mm; and bodyportion--0.25 mm.

Thus, as clearly shown in FIG. 6, the hinge portion shows substantialthickening over the heel portion. In accordance with the configurationof the aforesaid U.S. Pat. No. 4,785,948, eversion is prevented byrendering the heel thicker and rigid so that in attempting to bulgeaxially outward under pressure the base will be kept from doing so bythe rigidity of the heel. This means that the entire heel region isrigid and any bulging of the heel plus conical part 46 is prevented.

However, compared to the known art, in the configuration of the presentinvention, the rigid, thickened portion is placed inwards to the hingeportion, leaving the heel and adjoining side wall flexible, even whilepreventing eversion. As a result, upon pressurizing the bottle, the heeland side wall will move outward and down forming an increased and morestable standing section while eversion is still prevented. The result islimited stability of the bottle in the empty, unpressurized state andsubstantially enhanced stability when pressurized due to rolling out ofthe heel, all without eversion of the base, which is precluded by thethickened hinge.

A thickened region will have reduced orientation, even with the improveddesign represented by U.S. Pat. No. 4,785,948. This in turn meansreduced impact resistance, i.e., brittleness. Fortuitous impact loadsoccur usually near the heel and hardly ever near the center. Thus,brittleness near the center is tolerable, while brittleness near theheel is not. In accordance with the present invention orientation at theheel and therefore ductility are increased due to the placement of thethickened portion well inward.

As schematically illustrated in FIG. 7 for the container in the emptycondition, conical portion 46 includes a radius of curvature X betweenupper region 53 and standing section 51, and heel portion 50 also has aradius of curvature Y. A representative embodiment for a two litercontainer in the empty condition is radius X varying from 24 to 27 mmand radius Y varying from 17 to 20 mm. In accordance with the presentinvention the ratio of radius X to radius Y should be from 0.75 to 2 andpreferably from 1 to 1.6. It has been found that maintaining this ratiowill enhance the stability of the bottom portion of the container.

It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare susceptible of modification of form, size, arrangement of parts anddetails of operation. The invention rather is intended to encompass allsuch modifications which are within its spirit and scope as defined bythe claims.

What is claimed is:
 1. A blow molded, biaxially oriented plasticcontainer comprising a neck portion defining an opening; a tubular bodyportion depending therefrom; an integral bottom portion depending fromthe tubular body portion; an axially, inwardly directed, generallyconical portion of said bottom portion having an upper region thereof,wherein said bottom portion includes a standing section on which thecontainer rests in the upright condition; wherein said bottom portionincludes a heel portion joining the standing section and the bodyportion and a hinge portion joining the conical portion and the standingsection; said container having means including a hinge portion wallthickness greater than the heel portion wall thickness wherein said heelportion is spaced outward and downward upon pressurizing the containerto provide a stable bottom portion and wherein the standing section ofsaid container upon pressurizing is larger than the standing section inthe unpressurized container so as to form a stable standing section andwherein the heel portion has a radius of curvature and the conicalportion has a radius of curvature between the upper region and thestanding section with the ratio of the radius of curvature of the heelportion to the conical portion varying from 0.75 to 2.0.
 2. A containeraccording to claim 1 wherein the hinge portion has a greater wallthickness than the body portion.
 3. A container according to claim 1with the wall thickness of the hinge portion being greater than the wallthickness of the upper region of the conical portion.
 4. A containeraccording to claim 1 wherein the container has continuous alterations inwall thickness with a regularly undulating cross section, wherein saidcontinuous alterations in wall thickness are provided on the tubularbody portion adjacent the bottom portion and extending onto the bottomportion.
 5. A container according to claim 1 wherein said bottom portionstanding section is converted from a standing section radius to astanding section surface upon pressurizing.
 6. A container according toclaim 1 wherein the ratio of wall thickness of the heel portion to thehinge portion is approximately 1:10.
 7. A container according to claim 1wherein the standing section, hinge portion, heel portion and conicalportion all have a curved configuration.
 8. A container according toclaim 3 wherein the heel portion is thicker than the upper region of theconical portion.
 9. A container according to claim 1 wherein the heelportion wall thickness is greater than the body portion.